as in treacherous
formal
causing harm in a way that is gradual or not easily noticed
Most people with this insidious disease have no idea that they are infected. an insidious enemy
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Recent Examples of insidious
Daniel Kaluuya stars as a Black photographer visiting his white girlfriend's parents and is terrified to discover the truly insidious reason for his invitation.
—
Brian Truitt, USA Today, 22 Jan. 2026
But by the late 1950s, ICBMs emerged – and these deadly intercontinental ballistic missiles presented North America with a more insidious (and for a long time, indefensible) threat.
—Barry Scott Zellen, Hartford Courant, 22 Jan. 2026
Creating Ambiguity Around Expectations Perhaps the most insidious form of hybrid creep is the lack of clear guidelines.
—Caroline Castrillon, Forbes.com, 21 Jan. 2026
Méndez Aguilar has been accused of orchestrating an insidious human trafficking ring that started back in July targeting indigent pregnant women.
—Kevin Maurer, Rolling Stone, 13 Jan. 2026
See All Example Sentences for insidious
Brian Truitt, USA Today, 22 Jan. 2026
But by the late 1950s, ICBMs emerged – and these deadly intercontinental ballistic missiles presented North America with a more insidious (and for a long time, indefensible) threat.
—Barry Scott Zellen, Hartford Courant, 22 Jan. 2026
Creating Ambiguity Around Expectations Perhaps the most insidious form of hybrid creep is the lack of clear guidelines.
—Caroline Castrillon, Forbes.com, 21 Jan. 2026
Méndez Aguilar has been accused of orchestrating an insidious human trafficking ring that started back in July targeting indigent pregnant women.
—Kevin Maurer, Rolling Stone, 13 Jan. 2026
See All Example Sentences for insidious
Recent Examples of Synonyms for insidious
Adjective
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Ah, but excitement can be fleeting in the treacherous era of AI, and the cafe’s clever marketing team admitted the Puerto Rican music star hadn’t actually been here.—
Linda Zavoral,
Mercury News,
5 Feb. 2026
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Neighbors said the intersection where this deadly crash happened is part of a stretch of road that often turns treacherous, and there are safety changes that need to be made to benefit pedestrians and drivers alike.—
Marissa Perlman,
CBS News,
5 Feb. 2026
Adjective
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These subtle changes allowed scientists to calculate the planet’s dimensions with unprecedented accuracy, refining measurements that had remained largely unchanged since the 1970s.—
Neetika Walter,
Interesting Engineering,
5 Feb. 2026
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The 100 percent cotton jean features a true mid-rise, straight-leg silhouette with a subtle wedgie fit.—
Angela Velasquez,
Sourcing Journal,
4 Feb. 2026
Adjective
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The racist imagery is strategically embedded within a larger narrative promoting false election fraud conspiracy theories, designed to dehumanize Black and brown voters as threats to democracy and to justify restricting their participation in elections.—
Los Angeles Times,
Los Angeles Times,
6 Feb. 2026
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The Iranian shadow fleet consists of tankers and associated companies that operate outside normal commercial channels, often using false identities, ship-to-ship transfers, and deceptive documentation to hide Iranian crude and refined products.—
Claire Carter,
The Washington Examiner,
6 Feb. 2026
Adjective
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This type of malware is often spread through fake software updates, malicious email attachments, compromised browser extensions or deceptive ads.—
Kurt Knutsson,
FOXNews.com,
3 Feb. 2026
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Bright sunshine on Sunday will be deceptive as highs will only reach the low to mid-20s.—
Steven Sosna,
CBS News,
3 Feb. 2026
Adjective
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Observing human behavior confirms that for some among us, the perfidious lust for unbridled power and the imposition of cruelty in its quest know no bounds and are bereft of human decency.—
A.O. Scott,
New York Times,
3 Feb. 2026
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However, this question has now been resurrected and amplified by conservatives as evidence of a perfidious lack of patriotism.—
Charlie Campbell,
Time,
2 Feb. 2026
Adjective
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Conversely, the state Attorney General's office believes applying the anti-nepotism law in this situation would be an incorrect and overly broad interpretation.—
David Bauerlein,
Florida Times-Union,
4 Feb. 2026
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The state’s attorneys said that too was incorrect.—
Los Angeles Times,
Los Angeles Times,
4 Feb. 2026
Adjective
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Mia’s giant bow dress is fabulous, but her hair is all wrong.—
Jason P. Frank,
Vulture,
31 Jan. 2026
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Which is why the reaction to Clemson coach Dabo Swinney blowing the whistle on Ole Miss coach Pete Golding for alleged tampering feels so wrong.—
Mike Bianchi,
The Orlando Sentinel,
31 Jan. 2026
Cite this Entry
“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 8 Feb. 2026.
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